 For divers following the rule, one third of the gas supply is planned for the outward journey, one third is for the return journey and one third is a safety reserve.However, when diving with a buddy with a higher breathing rate or a different volume of gas, it may be necessary to set one third of your buddy's gas supply as your remaining 'third'.This means that the turn point to exit is earlier, or that the diver with the lower breathing rate carries a larger volume of gas than he alone requires.